1. Field of the Invention
The present invention provides an illumination system for use in a projection device.
2. Descriptions of the Related Art
Light emitting diodes (LEDs) are gradually replacing ultra high pressure (UHP) mercury bulbs as light sources of projection devices because of the LEDs providing high efficiency in energy transformation, high degree of stability, long service life, capability of being instantaneously switched on/off and the like. When LEDs are adopted as the light source of a projection device, the design and arrangement of the optical elements thereof need to be considered to obtain a satisfactory light utilization ratio and satisfactory light distribution uniformity. A common approach is to directly use red LEDs, blue LEDs and green LEDs as the light source of the projection device, and lights of the LEDs are outputted after being optically coupled. However, it is known that green LEDs have a low light emission efficiency, while red LEDs have a high demand on heat dissipation, so if the red LEDs, the blue LEDs and the green LEDs are used as the light source of the projection device directly, then the quantities, arrangement and heat dissipation manners of the red LEDs, the blue LEDs and the green LEDs have to be adjusted appropriately to facilitate the adjustment of the color uniformity as a whole.
Furthermore, the LEDs per se are known as a kind of light source with both a large divergence angle and large etendue. Hence, if the etendue thereof cannot be reduced for more effective use of light, problems such as inadequate projection luminance of the projection device and failure to make the efficient use of light energy emitted from the LED will also arise.
In view of this, an urgent need exists in the art to provide a solution that can make efficient use of light energy generated by the LED to increase the efficiency of utilization of light by the projection device and improve the projection luminance of the projection device as a whole.